How to reach: To reach the tidal bench marks from I-80, take the Dumbarton Bridge West exit, then turn left on Thorton Avenue West, follow the signs to the wildlife refuge which will lead to a frontage road and then to the Old Dumbarton bridge. The bench marks are along the roadway of the Old Dumbarton bridge. The tide gauge was located at the SW end of the old State Road 84 bridge. Special use permit or authorization is required to visit the bench marks or the station.